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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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448                                ALASKAN GLACIER STUDIES
from 580 feet to 880 feet above the railway being made in the two miles from the mouth of the valley glacier to the end of the first large tributary on the south. The surface of the valley glacier is little crevassed and only slightly encumbered with moraine. The moraine extends farthest up the glacier on the northern margin. The crevasses were predominantly longitudinal and travel was easy in 1910 upon the long narrow seracs of the valley glacier.
Barren Portion of Bulb. The southern half of the bulb of Heney Glacier is free from moraine and slopes 10 to 20. There is a little debris in this basal ice, but the surface has scattered stones upon it. Near the glacier margin the bottoms of a few crevasses reach to the very bottom of the glacier, revealing ice layers which stand at a high angle.
The northwestern half of the bulb is thickly mantled with ablation moraine and its surface is a maze of knobs, kettles, ridges and hollows, with ice showing in little cliffs at a few localities. The surface rises gradually from 150 to 680 feet above the railway. The surface of this ablation moraine was everywhere slumping in 1910 and vegetation had nowhere taken root upon it, except in a narrow strip close to the forested portion of the bulb. Even here the plants were very young and were scattered, so that, in general, there was a sharp line of demarcation between the barren and the forested zones of the moraine-covered bulb.
Forested Portion of Bulb. All of the eastern end of the bulb (PL CLXXVHI) is thickly covered with ablation moraine, beneath which the presence of ice is only shown by infrequent areas of slumping. This portion of the glacier is completely covered with dense forest. Most of the trees are alders, but there are scattered cottonwoods and willows.
The Terminal Moraine. The terminal moraine (PL CLXXVIII) is followed by the railway from the lake south of Mile Post 75 to the curve just beyond Mile Post 77. The glacier has retreated half to seven-eighths of a mile from the moraine. Near Mile Post 75 and for over a mile to the south the glacier retains an advanced position so that no moraine has been exposed by melting. For a short distance beyond this, however, there is an independent morainic ridge, from which the glacier has receded about half a mile. This southern moraine is broad and low and partly covered with forest.
The northern portion of the moraine where followed by the railway, varies in width from a single, symmetrical, narrow ridge to a moraine belt nearly an eighth of a mile wide. The height ranges from 5 to 15 feet, for the lower ridges, to 40 or 50 feet. The ridges are crescentic and parallel to the former ice front, and sometimes contain small ponds and dry kettles. The material in different parts of the moraine is till, rounded outwash gravel, fine river silt, cross-bedded dune sand, and huge angular bowlders. In several localities the till overlies the dune sand or the large angular blocks rest upon stratified stream deposits, showing that there has been an advance after a period of retreat. In no case were the lower deposits at all weathered.
The Marginal Lakes. There are four large and several small lakes around the margin of Heney Glacier. These lakes have one wall of ice and one of terminal moraine. Three of them lie within the two areas of interior flat which this bulb glacier has developed upon, either side of the central ridge of ablation moraine. That the lakes have fluctuated in level is well shown in the southernmost, where there were minute, abandoned beach levels in 1910.
The southern interior flat contained an area of ground moraine which was crossed by a remarkable series of hundreds of low, parallel furrows and ridges (PI. CLXXX) of